(1) Field of the Invention
The present invention relates to glass antennas formed on/in glass substrates and manufacturing methods for the same.
(2) Description of the Related Art
Recently, automobiles often have high-frequency GPS (Global Positioning System) antennas and also antennas for receiving satellite radio waves of satellite digital broadcasting. Further, there has been a demand for other types of antennas for use in ETC (Electronic Toll Collection) systems which automatically charge for use of highways or toll roads, and for radio wave beacons in the VICS (Vehicle Information Communication System). As such types of antennas, there has been technology in which window glass of automobiles is used as a substrate, and patch antennas (planner antennas) are constructed.
FIG. 11 is a side view showing a construction of a high-frequency glass antenna for automobiles given as a previous planner antenna. FIG. 11 corresponds to FIG. 5 of the following patent document 1. In the glass antenna of FIG. 11, an antenna conductor 120 is formed on the outer surface of the widow glass 110 of an automobile, and a reflection conductor 210 is formed on an inner surface of the window glass in such a manner that the antenna conductor 120 and the reflection conductor 210 at least partly face each other.
Here, for the purpose of good reception of GPS signals, which are circular polarization signals, the antenna conductor 120 has an antenna pattern of a spiral shape. The end of the center of the spiral form is connected to a power supplier 130. The size of the antenna pattern is 58 mm×46 mm, and the width of the line is 1 mm, and the interval between the spiral antenna conductor 120 is 5 mm.
The size of the reflection conductor 210 on the window glass 110 is 120 mm×60 mm. The reflection conductor 210 is electrically connected to the earth of a non-illustrated receiver through the following: a leg portion 170, which is formed by metal fittings for attaching an insulation box 150 to the window glass 110; a ground of an amplifier circuit built in the insulation box 150; and an outer conductor of a coaxial cable 180 for transmitting the output of the amplifier circuit to the non-illustrated receiver. Further, an electric supply line is connected from a power supplier 130, which is electrically connected to the input unit of the above amplifier circuit, to a part of the antenna conductor 120 with a conductive material through a hole 220 provided in the window glass 110.
With the above arrangement, in the present automobile high-frequency glass antenna, radio waves radiated from the antenna conductor 120 to the window glass 110 are reflected by the reflection conductor 210 and radiated to the antenna conductor 120 (outside of the automobile), so that antenna gain is increased.
Next, FIG. 12 is a schematic side view showing a construction of a previous window glass for automobiles as another previous planner antenna. FIG. 12 corresponds to FIG. 1 of the following patent document 2. The automobile window glass 500 of FIG. 12 is a glass sheet to be installed in an automobile, and on the surface of the glass substrate 100, a heat-shielding film 400 for shielding sunlight is applied. In a region in which the heat-shielding film 400 is not applied, the inside antenna 200 faces the outside antenna 300 with the glass substrate 100 interposed therebetween. With this arrangement, even in the automobile window glass to which the heat-shielding film 400 reflecting radio waves is applied, it becomes possible to transceive high-frequency radio waves such as FM waves or higher.
Further, the following patent document 3 discloses a technique for printing wiring on glass sheets. In the technique, a glass substrate is laid over a metal board which is appropriate as a conductor pattern material. From above the glass substrate, YAG laser light is emitted with a desired image pattern corresponding to a desired conductor pattern. As a result, the metal board is fused by heat or evaporated, and a desired conductor pattern is transferred to the glass substrate by heat. In this manner, a stable conductor pattern which does not come off easily is printed on the glass substrate, without using any chemicals. As an application of this technique, the following patent document 3 discloses the way of printing antenna conductor patterns on the windshields of automobiles for receiving FM broadcasting.
The following patent document 4 is not an art relating to antennas, but it discloses technology (electromagnetic wave-shielding film) for preventing the leakage and the invasion of electromagnetic waves. This electromagnetic wave-shielding film is a laminated film, on whose opposite sides, a metal conductive layer and a two-dimensional line pattern-printed layer are symmetrically laminated with the basic film as the center layer, or is a laminated film in which such films are laminated. All the patterns on the metal conductive layers and on the printed layers are substantially the same, and the patterns overlap one another on the basis film (the metal conductive layer is covered by the printed layer, viewed from the opposite sides of the basic film). This construction provides a film with good electromagnetic wave-shielding characteristics.
[Patent Document 1] Japanese Patent Application Laid-open No. HEI 7-29916
[Patent Document 2] Japanese Patent Application Laid-open No. HEI 6-247746
[Patent Document 3] Japanese Patent Application Laid-open No. HEI 6-104551
[Patent Document 4] Japanese Patent Application Laid-open No. HEI 10-341093
However, if antennas are simply formed on the surface of window glass as in the above patent documents 1 and 2, or using the technology disclosed in the above patent document 3, a problem of lowering of antenna gain because of loss due to the thickness of glass is caused. That is, normal glass sheets have a conductive loss of approximately 0.02, which is comparatively large. Thus, loss increases in frequencies of the UHF band or higher. If antenna (and ground patterns) are provided on the opposite sides of a glass sheet, gain is lowered because of loss of the glass sandwiched therebetween.
Further, when the technology disclosed in the above patent document 4 is applied to form a conductor pattern on a film, thereby providing an antenna, it is only possible to provide linear antenna. Hence, it is extremely difficult to provide high-gain antennas like patch antennas in which reflection boards are utilized.